Mixer



May 9, 1967 c. D. FISHER 3,318,582

MIXER Filed Nov. 4, 1965 United States Patent O M 3,318,582 MIXER Chester Donald Fisher, Muncy, Pa., assiguor to Sprout, Waldron & Company,1nc., Muncy, Pa., a corporation of Pennsylvania Filed Nov. 4, 1965, Ser. No. 506,317 16 claims. (C1. 259-97) The present invention relates to mixing .apparatus suitable for mixing powdered or granular materials, and more particularly to vertical type mixers in which the materials to be mixed `are carried continuously upward through the central portion of the mixer by a conveyor, such as a screw, and are discharged radially into the upper end of the casing for gravity 4return to the lower part of the casing.

Mixers of the afore-mentioned type have proved quite satisfactory in producing thorough mixing where the particles to be mixed are of a relatively uniform size. However, a problem does exist when the Aparticles are non-uniform in weight and size, the problem being that upon the material being discharged radially from the conveyor into the upper portion of the casing, for gravity return to the lower part thereof, differences in particle Weight yand size cause segregation of the particles rather than an intimate mixing. This problem is effectively solved by providing a baffle located approximately midway between the discharge end of the conveyor and the outer wall of the casing. This solution is set forth in the Fisher Patent #2,731,248.

It should be understood that vertical mixers which carry material continuously upwardly through the central part of the mixer and then discharge the material radially into the casing have a primary use for mixing batches of material. In batch mixers, the amount of time neces sary to effect a uniform mixing of the material contained therein is dependent primarily upon the efliciency of mixing, or the ability of the apparatus to mix large quantities of material in a rapid and eliicient manner in the shortest period of time.

In view of the above, it is a principal object of the present invention to provide a vertical mixer that mixes batches of granular materials having either dilierent or the sarne particle size while obtaining a substantially uniform consistency of mix faster and more economically than has heretofore been possible in this type of mixer.

Another object of the present invention is to provide means permitting admittance of material to the conveyor at at least one point in the batch in addition to the material being moved up the conveyor from the bottom ofy the batch, thus assuring increased eiciency of mixing.

Still another object of the present invention is to provide a vertical mixer particularly adapted for handling dry materials, which mixer will operate equally efliciently both with materials of approximately the same particle size and weight and also with dry materials of comparatively widely different particle sizes and weights, and which will in either case :produce thorough and uniform miic'ng of the particles in a shorter period of time.

Other objects and a fuller understanding of the invention may be had by referring to the following specication and claims taken in conjunction with the accompanying drawing in which:

FIG. 1 is a fragmentary profile view of a vertical mixer constructed in accordance with the present invention;

FIG. 2 is 4an enlarged fragmentary sectional View taken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary profile view of another embodiment of a vertical mixer constructed in accordance with the present invention; v

3,318,582 Patented May 9, 1967 ICC FIG. 4 is an enlarged fragmentary prole view of a portion of the apparatus illustrated in FIG. 3;

FIG. 5 is a fragmentary sectional view of another embodiment of apparatus which may -be used in conjunction with the apparatus of FIGS. 1-4; and

FIG. 6 is a sectional view taken along line 6 6 of FIG. 5 and as if FIG. 5 were not in section.

Referring now to the drawing and particularly FIG. 1 thereof, ya mixer 1i) having a vertically oriented casing 11 including a cylindrical upper portion 12 and a lower funnel portion 13, is illustrated therein. A top wall 14 and bottom wall 15 close the casing 11 and allow the casing to retain interiorly thereof a load of granular material to be mixed. The lower or funnel portion 13 of the casing 11 is provided with a discharge spout 16 which may be suitably valved to provide gravity discharge of the material upon completion of mixing. Mounted interiorly of the casing 11 and substantially coaxially therewith, is a mixing tube 30 constructed in accordance with the present invention, and supported by struts 9 so that the upper and lower or discharge and inlet terminal ends 31 and 32 of the tube are spaced respectively from the top and bottom walls 14 and 15 of the casing 11.

In order to provide lifting of the material to be Imixed from the lower or funnel portion 13 of the casing 11 to the upper portion 12, a conveyor 17, in the present instance a screw or worm 18 extends vertically through the casing. The screw 18 is rotatably mounted in the bottom wall 15 and in the present instance connected at its upper end, externally of the top wall 14, to drive means 19 including a motor 20 whichthrough belts 21 turn pulleys 22 connected to the screw 18. A-s illustrated in FIG. 1, the upper terminal end 31 of the mixing tube 3i) provides the discharge opening for the material being conveyed up the tube by the conveyor 17, and radially extending flinger paddles 33, mounted on the sha-ft of the screw 1S between the top wall 14 and the discharge opening for rotation with the screw, operate to throw the material radially outwardly into the surrounding upper portion 12 of the casing 11.

In accordance with the invention, means are provided axially of the mixing tube 30, at least at one point other than the inlet end 32 thereof, to provide a multiple level input into the conveyor effectuating an increase in the efciency of mixing of the material thus to be treated. To this end, at least one, in the present instance a plurality of both circumfentially and axially spaced apertures 34 lare provided in the wall of the mixing tube 30 to permit entry into the rotating screw conveyor 18. In addition, so as to provide a free ow and good metering of the material as it enters into the mixing tube 30 through the apertures 34, and in order to meter the lmaterial properly to draw the material into the mixing tube and up the conveyor, the screw 18 is preferably of the variable pitch variety, in the present instance the variation in pitch occurring in steps. For example, the conveyor 18 illustrated in FIG. 1 has four such changes in pitch occurring between the bottom wall 15 and the discharge end 31 of the mixing tube 30, which change occurs from the liner pitch at the bottom to the coarser pitch at the upper end of the screw in order to accommodate the increased quantity of material being conveyed to the discharge -or upper terminal end 31 of the mixing tube 30. For example, in FIG. 1 the screw 18 hasfour sections of ilights with varying pitches which have been designated 18a-18d for purposes of identification. By way of example, if the diameter of the screw is 12 inches, the section of the screw having the finer pitch, 18a may be at 1/3 or 4 inches pitch, the section having a pitch designated 181, may be at 1/2 pitch or 6 inches, while the section having a pitch designated 18c may be at pitch or 8 inches and the final pitch of 18d may be a full pitch of 12 inches.

The mixer 1i) illustrated in FIG. 1 is particularly adapted for mixing efliciently large granular substances. For example, it has been found that when extruding from several machines a plastic such as polyethylene, chopping or cutting the plastic into small particles for example approximately 1A; of an inch in diameter, the meld index (melting point) of the polyethylene thus extruded and cut will be different from each of the machines. Thus prior to subsequent treatment it is necessary to mix the particles in a mixer such as heretofore described to obtain a uniformity of end product for subsequent treatment. If however the weights and sizes vary somewhat, it may be preferable to insure that the material being discharged through the upper terminal end 31 of the mixing tube 30 is not segregated. This may occur because the heavier particles tend to drop near the center of the casing while the smaller particles tend to pass outwardly therebeyond towards the Y outer wall of the casing. With particles of varying weights it is preferable to mount a distributor or baille unit 40 at the upper portion of the casing 11 to prevent segregation of the material. An example of a baflle unit which will prevent segregation is described in the Fisher Patent #2,731,248, which for purposes of clarification is briefly described below.

The baffle unit typically includes a cylindrical upper portion 41 secured to and depending from the top wall 14 and having la lower terminus somewhat below the discharge end 31 of the mixing tube 30. As illustrated, the cylindrical upper portion 41 is serrated to provide a plurality of open spaces 42 alternating with solid baille members 43. The open spaces 42 and the baille solid portions 43 are arranged so as to have an approximately equalV angular dimension and alternate circumferentially of the Vmixer. With a baffle constructed in this manner, the solid materials lifted by the screw to the top of the mixing tube 30 will be flung radially outwardly by the rotating paddles 33 with sufiicient force to carry to the outside wall of the casing. However the solid baflle portions 43 will intercept approximately 50% of the discharge material while the remainder of the material will pass through the openings 42. In this manner an -averaging of the discharge material across the radius and around the circumference of the casing takes pl-ace. In addition, in certain instances and under some conditions it is desirable to place an additional solid baille radially outwardly of the baille 40, the addi- Ational baflle'44 being of a circumferentially continuous construction.

Thus when mixing a material of uniform granular size and weight, the baille such as above described is not necessary while if the Vgranular size and/ or weight vary, -a baille such as above described may be preferable to obtain va uniform mix.

When Vmixing large granular particles such as polyethylene pellets approximately 1/8 of an inch in size with a fine granular material such as a powder, a mixture results that has poor flow characteristics. In addition, mixtures of powders of relatively fine size, generally have poor flow characteristics. Such mixtures have a tendency toV form arches and not llow freely at the break between the cylindrical portion 12 and the funnel portion 13 of the mixer. If the materials do not flow freely at this break between the cylinder and the cone, a poor mix of this portion of a non-flowing material will be obtained from the mixer. This problem may be circumvented by modifying the apparatus in accordance with the present invention. Such a modified apparatus is illustrated in FIGS. 3 and 4 and includes a mixing tube 130 having a variable pitch screw 118 rotatably mounted therein, in the present instance a two-step conveying screw. At the lower portion of the tube 130 is a radial enlargement 135 having an outwardly VVand downwardly flared upper portion 135a and, in the present instance, an inwardly tapered or inverted conically shaped lower portion 135b. As illustrated the inverted cone 1351 is located on the center tube 130 at the approximate critical junction between the cylindrical portion 12 and thev funnel shaped portion 13. With the addition of the inverted cone 13Sb on the center tube 130, the tendency to arch at the critical break between the cylindrical portion 12 and the funnel shaped portion 13 is prevented, and the two non-free flowing types of mixes described above will pass freely down between the space between the funnel portion 13 and the inverted cone 135b into the elevating screw at the inlet 132.

In order to provide a ow of material into tube in addition to the material entering the inlet end 132 of the tube, the outwardly and downwardly tapered portion 135:1 is provided with a plurality of cir-V cumferentially spaced apertures 134, in the presentinstance in the same radial plane, leading into an inverted conical passageway 136. Because of the outward flare of the portion 13511, the apertures 134 will permit quantities of `substantially uniform grain size of fine, non-free flowing powder, or a mixture of fine non-free flowing powder and larger granular material, to enter unimpeded into the passageway 136 and thus enter the flights of the screw conveyor 118. An example of the type of material which could be mixed effectively with a mixer such as heretofore `described with reference to FIGS. 3 and 4 is the large sized polyethylene .granulars, above discussed, with a powdered granular coloring material.

It should be recognized that in utilizing a mixer such as illustrated in FIGS. 3 and 4 with a material that is Vto be mixed which includes a large granular substance and a powdered or line non-free flowing powder, a baille 140, similar to the baille 40 such as heretofore described, is desirable so as to prevent stratification or segregation of the powder and the large particles. However, in the instance where a fine powder such as a polyethylene plastic powder is to be mixed with other fine powders, such as polyvinyl chloride powders, pharmaceutical powders,

metallic oxides or the like, it has been found that theV baille such as heretoforedescribed, although not impeding the mixing process, is unnecessary andV may be. dispensed with.

In order to provide a free flow of material into Veither the mixing tube 30 associated with the mixer 10 illustrated in FIG. 1 or the mixing tube 130 associated with the mixer shown in FIG. 3, it may be desirable to modify the apertures 34 as.illustrated in FIGS. 5 and 6.- To

this end, an aperture 234 is illustrated as having an outwardly projecting or protruding, semi-conical lip portion l 235 which form a chute-like pocket 236 permitting a free flow of material from the casing into the, mixing ktube without the risk of bridging or clogging of the aperture,V

Thus the apparatus of the present invention permits of more uniform mixing by providing passageways which permit a flow of material into the mixing tubeV at at` construction, and the combination and arrangementV of partsV may be made without departing from the spirit and Y scope of the invention as hereinafter claimed.

What is claimed is: Y

1. A mixer for mixing granular materials comprising: a substantially vertical casing having a top wall and a bottom wall connected thereto, a mixing tube supported in said casing naving an upper discharge and lowerinlet end spaced from said top wall and said bottom wall respectively, a variable pitch conveying screw mounted in said tube for moving said material up said tube from said inlet to said outlet, saidscrew having a finer pitch at said inlet than at said outlet, a radial enlargement connected to said mixing tube and having an outwardly and downwardly flared upper portion, a plurality of circumthe mixing f ferentially spaced apertures positioned in said flared portion to provide a passageway for the oW of said material in said casing into the conveying screw.

2. A mixer for mixing granular materials in accordance with claim 1 including an inverted conical passageway connecting said apertures with said screw.

3. A mixer for mixing granular materials in accordance with claim 1 including an inverted conically shaped lower portion connected to said downwardly dared upper portion.

4. A mixer for mixing granular materials in accordance with claim 3 wherein said casing comprises a cylindrical upper portion and a funnel shaped lower portion, and wherein said inverted conical portion is located approximately at the break between said cylindrical upper portion and said funnel shaped lower portion to prevent arching of non-free owing materials being mixed in said mixer.

5. A mixer for mixing granular materials in accord-ance with claim 1 including radially extending inger paddles mounted on said conveying screw between said discharge end of said tube and said top Wall for ilinging material radially from said discharge end.

6. A mixer for mixing granular materials in accordance with claim 5 including a battle secured to and depending `from said top wall, said baiile having a plurality of open spaces alternating with solid baffle members and located circumferentially of the casing.

7. A mixer for mixing granular materials comprising: a substantially vertical casing having a top wall and a bottom wall connected thereto, a mixing tube supported in said casing having an upper discharge and lower inlet end spaced from said top wall and said bottom wall respectively, a variable pitch conveying screw mounted in said tube for moving said material up said tube from said inlet to said outlet, said conveying screw having a ner pitch at the inlet end of said tube and a coarser pitch at the discharge end of said tube, and .a plurality of circumferentially and axially spaced apertures in said tube to provide passageways for the ow of said material into said tube at various axial levels of said tube.

8. A mixer for mixing granular materials in accordance with claim 7 wherein at least some of said apertures have an outwardly projecting lip portion forming a chute-like pocket for passing material from said casing into said conveying screw.

9. A mixer for mixing granular materials in accordance with claim 7 including radially extending flinger paddles mounted on said conveying screw between said discharge end of said tube and said top wall for inging material radially from said discharge end.

10. A mixer for mixing granular materials in accordance with claim 7 including a bathe secured to and depending from said top wall, said bale having a plurality of open spaces alternating with solid baille members and located circumferentially of the casing.

11. A mixer for mixing granular materials comprising:

a substantially vertical casing having a top wall and a bottom wall connected thereto, a mixing tube supported in said casing having an upper discharge and lower inlet 5 end spaced from said top wall and said bottom wall respectively, a variable pitch conveying screw mounted in said tube for moving material up said tube from said inlet to said outlet, said tube having a radial enlargement adjacent the inlet end of said tube, said enlargement having an outwardly and downwardly ared upper portion and a plurality of circumferentially spaced apertures in said ared portion, .an inverted conical passageway connecting said apertures with said conveying screw to provide a ow of material from said casing into said conveying screw.

12. A mixer for mixing granular materials in accordance with claim 11 including radially extending inger paddles mounted on `said conveying screw between said discharge end of said tube and said top wall for inging material radially from said discharge end.

13. A mixer for mixing granular materials in accordance with claim 11 including a baille secured to and depending from said top wall, said baffle having a plurality of open spaces alternating with solid baille members and located circumferentially of the casing.

14. A mixer for mixing granular materials in accordance with claim 11 including an inverted conically shaped lower portion connected to lsaid downwardly flared upper portion.

15. A mixer for mixing granular materials in accordance with claim 14 wherein said casing comprises a cylindrical upper portion and a funnel shaped lower portion, and wherein said inverted conical portion is located approximately at the break between said cylindrical upper portion and said funnel shaped lower portion to prevent arching of non-free flowing materials being mixed in said mixer.

16. A mixer for mixing granular material in accordance with claim 7 wherein said variable pitch screw is stepped having at least two variations in pitch.

1/1956 Fisher 259-97 ll/1965 Goins 222-459 FOREIGN PATENTS 4/ 1923 Germany. 4/ 1946 Great Britain. 7/ 1955 Italy.

WALTER A. SCHEEL, Primary Examiner.

R. W. JENKINS, Assistant Examiner. 

1. A MIXER FOR MIXING GRANULAR MATERIALS COMPRISING: A SUBSTANTIALLY VERTICAL CASING HAVING A TOP WALL AND A BOTTOM WALL CONNECTED THERETO, A MIXING TUBE SUPPORTED IN SAID CASING HAVING AN UPPER DISCHARGE AND LOWER INLET END SPACED FROM SAID TOP WALL AND SAID BOTTOM WALL RESPECTIVELY, A VARIABLE PITCH CONVEYING SCREW MOUNTED IN SAID TUBE FOR MOVING SAID MATERIAL UP SAID TUBE FROM SAID INLET TO SAID OUTLET, SAID SCREW HAVING A FINER PITCH AT SAID INLET THAN AT SAID OUTLET, A RADIAL ENLARGEMENT CONNECTED TO SAID MIXING TUBE AND HAVING AN OUTWARDLY AND DOWNWARDLY FLARED UPPER PORTION, A PLURALITY OF CIRCUMFERENTIALLY SPACED APERTURES POSITIONED IN SAID FLARED PORTION TO PROVIDE A PASSAGEWAY FOR THE FLOW OF SAID MATERIAL IN SAID CASING INTO THE CONVEYING SCREW. 